Bié(別), bú yào(不要) and béng(甭) can be used in the negative imperative sentences with or without the subject.
Bié(別) and bú yào(不要) share the same meaning when used to forbid or dissuade somebody from doing something. The imperative sentences introduced by bú yào (不要) are stronger in tone than these start with bié(別).
yǔ zhè me dà, nǐ bié/bú yào chū mén le.
It's raining hard, don't go out.
bú yào /bié dà shēng jiǎng huà!
Don't talk loudly!
The negative adverb bié(別) also could be used in negative imperative sentences expressing the assumption of an undesirable situation. The expression usually is bié(shi)别(是)+ the undesirable situation.
yuē dìng de shí jiān dōu guò le, bié shì tā bù lái le ba?
The appointed time passed, could it be that he is not coming?
The pronunciation of béng(甭) is the combination of the pronunciations of bù (不) and yòng (用), which conveys the meaning of “don’t need to”.
jì rán nǐ dōu zhī dào le, wǒ jiù béng shuō le.
Now you know all about it, I don’t need to say anything.
Béng(甭) also dissuade somebody from doing something, in this case, bié(別), bú yào(不要) and béng(甭) are interchangeable.
nǐ bié /béng /bú yào lǐ tā, tā zhè gè rén yī zhí zhè me tǎo yàn.
Forget him, he has always been such a nuisance.